Preparation And Performance Study Of Electrode Materials For Supercapacitors By Biomass Porous Carbon Composite Transition Metal Oxidation

With the development of economy and society,environmental and energy problems of our country are becoming increasingly serious,which bring unprecedented challenges to human survival.Supercapacitors have high energy density and power density,long cycle life,rapid charge and discharge,and friendly environment.These advantages can make up for the defects of traditional capacitors and batteries,and effectively solve the two major problems of environment and energy.Electrode material is the fundamental factor to determine the of supercapacitor performance.Therefore,the development of electrode materials with high capacitance and low cost has become a research hotspot.Transition metal oxides have possess the high theoretical specific capacitance,and biomass derived carbon materials have the advantage of low cost,high conductivity and stability.Hence,in this paper,the biomass porous carbon（BPC）was prepared from pomelo peel as a carbon source to compensate for the poor conductivity and stability of cobalt oxide（Co₃O₄）and nickel cobalt oxide（Ni Co₂O₄）.The main research contents are as follows:（1）Taking pomelo peel as the biomass carbon source,the specific surface area and pore size of the carbon material were effectively regulated by controlling the ratio of precarbonized carbon and activator KOH,,and the BPC was prepared by combining pyrolysis and chemical activation processes.The relationship between the microscopic pore structure and electrochemical properties has been further investigated.The experimental results indicate that:BPC₃ has abundant pore structure,large specific surface area(1713.78 m~2 g^-1)and excellent properties.As the current density is 1 A g^-1,the specific capacitance of BPC₃ is up to 240.67 F g^-1,which is much higher than that of BPC₂(186.85 F g^-1)and BPC₄(161.24 F g^-1).When the current density increases from 1 A g^-1 to 10 A g^-1,the BPC₃ specific capacitance rate is 68.14%.when the charge-discharge cycle is tested 3000 times at the current density of 10 A g^-1,the specific capacitance retention of BPC₂,BPC₃ and BPC₄ can reach 100%.（2）In order to make up for the disadvantage of the low specific capacity of biomass porous carbon materials,the BPC₃ doped Co₃O₄ composites（Co₃O₄@BPC₃-X/NF）were prepared by sacrificial template method using nickel foam,cobalt nitrate,2-methylimidazole and BPC₃ as raw materials.The chemical composition,morphology,elemental valences,and electrochemical energy storage characteristics of the materials were detected by characterization tests.The results show that Co₃O₄@BPC₃-X/NF possess hollow leaf structure,and Co element exists in the form of Co²⁺and Co³⁺in Co₃O₄@BPC₃-1/NF composite.Among all the prepared samples,the Co₃O₄@BPC₃-1/NF composite electrode material has high specific capacitance(268.25 F g^-1when the current density is 1 A g^-1).good specific capacitance rate(75.97%when the current density increases from 1 A g^-1 to 10 A g^-1),and excellent cycle stability(when the current density is 10 A g^-1,the specific capacitance retention rate is 96.71%after 3000 times charge-discharge cycle).（3）In order to further improve the specific capacity of the composite electrode material,Ni Co₂O₄composite（Ni Co₂O₄@BPC₃-X/NF）doped with BPC₃ was successfully prepared by using nickel foam,nickel nitrate,cobalt nitrate,urea and BPC₃ as raw materials through simple hydrothermal and high-temperature heat treatment.The experimental results demonstrate that Ni Co₂O₄@BPC₃-X/NF possess nano-needle structure.The Ni and Co elements in Ni Co₂O₄@BPC₃-5/NF were existed in the form of Ni²⁺/Ni³⁺and Co²⁺/Co³⁺,respectively,and the content of BPC₃ was about 0.86 wt%.Ni Co₂O₄@BPC₃-5/NF has a high specific capacitance(392.20 F g^-1 when the current density is 1 A g^-1),good specific capacitance rate(84.25%when the current density increases from 1 A g^-1 to 10 A g^-1)and excellent cycle stability(the specific capacitance retention is 93.51%after 3000 charge/discharge cycles when the current density is10 A g^-1).